[gradsusr] Fwd: Re: Saving NetCDF lon parameter in geographic
Charles Seman
charles.seman at noaa.gov
Thu Apr 12 17:49:39 EDT 2012
Mark,
a typo in my comments below:
...so the output file runs from longitude = 0.125,...,359.8755
should be
...so the output file runs from longitude = 0.125,...,359.875
Sorry for the confusion,
Chuck
-------- Original Message --------
Subject: Re: [gradsusr] Saving NetCDF lon parameter in geographic
Date: Thu, 12 Apr 2012 17:44:16 -0400
From: Charles Seman <charles.seman at noaa.gov>
To: GrADS Users Forum <gradsusr at gradsusr.org>
Mark,
The documentation at
http://grads.iges.org/grads/gadoc/gradcomdsdfwrite.html states:
"By default, the output file will have a coordinate variable only for
varying dimensions in the defined variable; non-varying dimensions will
not appear as a coordinate variable with a size of 1. However, as of
version 2.0.a5, options have been added to the set sdfwrite command to
force the variable in the output file to have at least 4 or all 5
dimensions. When either of these options to set sdfwrite are used, the
output file will retain information about the values of the dimensions
that were fixed when the variable was defined; non-varying dimensions
will appear as a coordinate variable of size 1. For example, if your
defined variable is 500mb height on14may2002 (a 2D variable that varies
only in lon and lat), and you use the -4d option, the output file with
show height as a 4D variable with a Z dimension of size 1 called 'lev'
with a value "500 mb", and a T dimension of size 1 called 'time' with a
value of "0 minutes since 2002-05-14 00:00".
Seems the key phrase seems to be "the output file will retain
information about the values of the dimensions that were fixed when the
variable was defined"... I confirmed what I thought this meant on a file
which has grid longitudes in the -180 to 180 range and found the
following results:
--------------------------------------------------------------------
...using "native" longitude range:
ga-> sdfopen 3B42.1002.V6.nc
Scanning self-describing file: 3B42.1002.V6.nc
SDF file 3B42.1002.V6.nc is open as file 1
LON set to 0 360
LAT set to -49.875 49.875
LEV set to 0 0
Time values set: 2010:2:14:22 2010:2:14:22
E set to 1 1
ga-> q file
File 1 : NASA TRMM 3B42 3-Hourly 0.25 degree TRMM and Other Satellites
Precipitation Product (Version 6)
Descriptor: 3B42.1002.V6.nc
Binary: 3B42.1002.V6.nc
Type = Gridded
Xsize = 1440 Ysize = 400 Zsize = 1 Tsize = 1 Esize = 1
Number of Variables = 2
precipitation 0 t,y,x precipitation
relativeerror 0 t,y,x relativeError
ga-> set lon -180 180
LON set to -180 180
ga-> set lat -90 90
LAT set to -90 90
ga-> set sdfwrite precipitation.3B42.1002.V6.nc
SDFWrite file name = precipitation.3B42.1002.V6.nc
SDFWrite will replace an existing file
ga-> sdfwrite precipitation
SDFWRITE error: no defined variables
ga-> define precipitation = precipitation
Define memory allocation size = 8328992 bytes
ga-> sdfwrite precipitation
Wrote variable precipitation to precipitation.3B42.1002.V6.nc
...
cjs: /tmp/data/precip/trmm/3B42.V6/pp/0.25x0.25/av/monthly/update/ -->
\ncdump -c precipitation.3B42.1002.V6.nc
netcdf precipitation.3B42.1002.V6 {
dimensions:
longitude = 1442 ;
latitude = 722 ;
...
longitude = -180.125,...,180.125
latitude = -90.125,...,90.125
...
...so the output file runs from longitude = -180.125 to 180.125 and from
latitude = -90.125 to 90.125 (a couple extra points added in each
direction, so be careful)
--------------------------------------------------------------------
--------------------------------------------------------------------
...using a "global" longitude range, using x,y coordinates to define
exact boundaries:
ga-> sdfopen 3B42.1002.V6.nc
Scanning self-describing file: 3B42.1002.V6.nc
SDF file 3B42.1002.V6.nc is open as file 1
LON set to 0 360
LAT set to -49.875 49.875
LEV set to 0 0
Time values set: 2010:2:14:22 2010:2:14:22
E set to 1 1
...
ga-> set y 1 400
LAT set to -49.875 49.875
ga-> set x 721 2160
LON set to 0.125 359.875
ga-> set sdfwrite precipitation.3B42.1002.V6.nc
SDFWrite file name = precipitation.3B42.1002.V6.nc
SDFWrite will replace an existing file
ga-> define precipitation = precipitation
Define memory allocation size = 4608000 bytes
ga-> sdfwrite precipitation
Wrote variable precipitation to precipitation.3B42.1002.V6.nc
cjs: /tmp/data/precip/trmm/3B42.V6/pp/0.25x0.25/av/monthly/update/ -->
\ncdump -c precipitation.3B42.1002.V6.nc
netcdf precipitation.3B42.1002.V6 {
dimensions:
longitude = 1440 ;
latitude = 400 ;
longitude = 0.125,...,359.875
latitude = -49.875,...,49.875
...
...so the output file runs from longitude = 0.125,...,359.8755 and from
latitude = -49.875,...,49.875
--------------------------------------------------------------------
Could you try defining the variable to sdfwrite using parameters
appropriate to the netCDF file's original grid?
Hope this helps,
Chuck
On 04/12/2012 03:57 PM, Mark Hess wrote:
> I have a NetCDF file which I can ingest and display in GrADS with out a
> problem. The LON parameter is set to a 0-360 grid as opposed to 0-180W &
> 0-180E (or 0 to 180 for east and 0 to -180 for west). If I "set lon 239
> 244" and then display my variable of interest (in this case U), the data
> display properly showing the data between 116W-121W (116W equaling
> -116=244-360 and 121W equaling -121=360-239). That all is fine until I
> try to save my geographically subsetted area to a new .nc file using the
> sdfwrite function. The file saves fine, but it saves the LON information
> in the 0-360 format instead of the 0 to -180 format which I need for
> another application. Is there a way to either 1) save the new, subsetted
> .nc file with the lons converting to the in 0 to -180 format as part of
> the process or 2) convert the lon format within GrADS first and then
> save the new .nc file with the lon values in the format I want? Can I
> subtract 360 from my "lon" variable to create a 'new' lon variable?
> Thanks,
> Mark
>
>
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--
Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.
********************************************************************
Charles Seman Charles.Seman at noaa.gov
U.S. Department of Commerce / NOAA / OAR
Geophysical Fluid Dynamics Laboratory voice: (609) 452-6547
201 Forrestal Road fax: (609) 987-5063
Princeton, NJ 08540-6649 http://www.gfdl.noaa.gov/~cjs/
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